This invention relates to heat-recoverable articles and methods for their use.
Heat-recoverable articles, especially heat-shrinkable articles, are now widely used in many areas where insulation, sealing and encapsulation are required. Usually these articles recover, on heating, towards an original shape from which they have been previously deformed, but the term "heat-recoverable" as used herein also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.
Heat-recoverable articles are typically made from polymeric materials exhibiting the property of plastic or elastic memory as described, for example, in U.S. Pat. Nos. 2,027,962 and 3,086,243. In other articles, as described, for example, in British Pat. No. 1,440,524, an elastomeric member such as an outer tubular member is held in a stretched state by a second member, such as an inner tubular member, which, upon heating, weakens and thus allows the elastomeric member to recover. Finally, it has more recently been found that heat-recoverable articles can also be made from certain metal alloys. Such alloys, sometimes called "memory metals", are described for example in U.S. Pat. Nos. 3,174,851 and 3,351,463, and the book "Shape Memory Effects in Alloys" Jeff Perkins, Plenum Press, New York and London, 1975.
In many applications, especially those related to the installation and repair of supply lines such as electricity cables and gas pipes, the heat-recoverable articles are exposed to contaminants such as insects, moisture, gas leaks etc. which may damage or interfere with the functioning of the articles themselves and/or associated equipment. In general the material of the heat-recoverable article and its design ensure that the contaminants are excluded after recovery but problems may arise during storage and transport of the articles and/or in applications, such as the wall feed-through device described and claimed in British Pat. No. 1,245,119, where the heat-recoverable article may be installed on site some time before recovery is effected.
In yet other applications, it may be desirable to effect recovery of one portion of a heat-recoverable article whilst avoiding premature recovery of another portion. Amongst such articles there may be mentioned, for example, distribution caps for junction boxes in cable television systems such as CATV (Consumer Antenna Television). These distribution caps have a plurality of heat-shrinkable conduits each adapted to receive and, on heating, grip, a cable passing into the junction box. The number of cables passing into a given box may vary from area to area or from time to time, with the result that it may not be necessary to employ all of the conduits or that it may be desirable to employ some of the conduits during a first operation and others in a second, later operation. A serious problem arises, however, in that the necessary close proximity of the conduits makes it difficult, if not impossible, selectively to recover some of the conduits by heating without simultaneously at least partially shrinking the others.
Another article of this sort is a telephone exchange distribution box. A multicore cable comprising many individual wires is led into such a box, the unused wires being capped and remaining within the box whilst the other wires are led out through conduits which are heat-recovered to hold the wires in place and to seal the box. Further heat-recoverable conduits are, of course, provided for future use of the capped wires.